The electrochemical reduction of CO₂ is an extremely potential technique to achieve the goal of carbon neutrality, but the development of electrocatalysts with high activity, excellent product selectivity, and long-term durability remains a great challenge. Herein, the role of metal-supports interaction (MSI) between different active sites (including single and bimetallic atom sites consisting of Cu and Ni atoms) and carbon-based supports (including C₂N, C₃N₄, N-coordination graphene, and graphdiyne) on catalytic activity, product selectivity, and thermodynamic stability towards CO₂ reduction reaction (CRR) is systematically investigated by first principles calculations. Our results show that MSI is mainly related to the charge transfer behavior from metal sites to supports, and different MSI leads to diverse magnetic moments and d-band centers. Subsequently, the adsorption and catalytic performance can be efficiently improved by tuning MSI. Notably, the bimetallic atom supported graphdiyne not only exhibits a better catalytic activity, higher product selectivity, and higher thermodynamic stability, but also effectively inhibits the hydrogen evolution reaction. This finding provides a new research idea and optimization strategy for the rational design of high-efficiency CRR catalysts.

Linear relations between the adsorption free energies of nitrogen reduction reaction (NRR) intermediates limit the catalytic activity of single atom catalysts (SACs) to reach the optimal region. Significant improvements in NRR activity require the balance of binding strength of reaction intermediates. Herein, we have investigated the C₃N-supported monometallic (M/C₃N) and bimetallic (M₁M₂/C₃N) atoms for the electrochemical NRR by using density functional theory (DFT) calculations. The results show that this linear relation does exist for SACs because all the intermediates bind to the same site on M/C₃N. But the synergistic effect of the two atoms in M₁M₂/C₃N can create a more flexible adsorption site for intermediates, which results in the decoupling of adsorption free energies of key intermediates. Subsequently, the fundamental limitation of scaling relations on limiting potentials is broken through. Most notably, the optimal limiting potential is increased from −0.63 V for M/C₃N to −0.20 V for M₁M₂/C₃N. In addition, the presence of bimetallic atoms can also effectively inhibit the hydrogen evolution reaction (HER) as well as improve the stability of the catalysts. This study proposes that the introduction of bimetallic atoms into C₃N is beneficial to break the linear relations and develop efficient NRR electrocatalysts.

Carbon-supported transition metal single atoms are promising oxygen reduction reaction (ORR) electrocatalyst. Since there are many types of carbon supports and transition metals, the accurate prediction of the components with high activity through theoretical calculations can greatly save experimental time and costs. In this work, the ORR catalytic properties of 180 types single-atom catalysts (SACs) composed of the eight representative carbon-based substrates (graphdiyne, C₂N, C₃N₄, phthalocyanine, C-coordination graphene, N-coordination graphene, covalent organic frameworks and metal-organic frameworks) and 3d, 4d, and 5d transition metal elements are investigated by density functional theory (DFT). The adsorption free energy of OH* is proved a universal descriptor capable of accurately prediction of the ORR catalytic activity. It is found that the oxygen reduction reaction overpotentials of all the researched SACs follow one volcano shape very well with the adsorption free energy of OH*. Phthalocyanine, N-coordination graphene and metal-organic frameworks stand out as the promising supports for single metal atom due to the relatively lower overpotentials. Notably, the Co-doped metal-organic frameworks, Ir-doped phthalocyanine, Co-doped N-coordination graphene, Co-doped graphdiyne and Rh-doped phthalocyanine show extremely low overpotentials comparable to that of Pt (111). The study provides a guideline for design and selection of carbon-supported SACs toward oxygen reduction reaction.

Due to the high specific surface area, abundant nitrogen and micropores, ZIF-8 is a commonly used precursor for preparing high performance Fe-N-C catalysts. However, the Zn element is inevitably remained in the prepared Fe-N-C catalyst. Whether the residual Zn element affects the catalytic activity and active site center of the Fe-N-C catalyst caused widespread curiosity, but has not been studied yet. Herein, we built several Fe, Zn, and N co-doped graphene models to investigate the effect of Zn atoms on the electrocatalytic performance of Fe-N-C catalysts by using density functional theory method. The calculation results show that all the calculated Fe-Zn-N_x structures are thermodynamically stable due to the negative formation energies and relative stabilities. The active sites around Fe and Zn atoms in the structure of Fe-Zn-N₆(III) show the lowest oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) overpotentials of 0.38 and 0.43 V, respectively. The bridge site of Fe-Zn in Fe-Zn-N₅ shows the lowest η^HER of −0.26 V. A few structures with a better activity than that of FeN₄ or ZnN₄ are attributed to the synergistic effects between Fe and Zn atoms. The calculated ORR reaction pathways on Fe-Zn-N₆(III) show that H₂O is the final product and the ORR mechanism on the catalyst would be a four-electron process, and the existence of Zn element in the Fe-N-C catalysts plays a key role in reducing the ORR activation energy barrier. The results are helpful for the deep understand of high-performance Fe-N-C catalysts.